The present invention relates to dilatation balloon catheters employed in percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) procedures, and more particularly to the means for forming fluid tight seals between these catheters and their associated dilatation balloons.
Balloon catheters are well known for their utility in treating certain types of obstructions or occlusions in blood vessels, such as plaque build up. Angioplasty catheterization typically involves aligning a balloon catheter within the vessel to position its dilatation balloon at or along the obstruction. Then, fluid under pressure is supplied to the balloon through a balloon inflation lumen in the catheter, expanding the balloon against the obstruction.
In the manufacture of balloon catheters, it is essential that the bonds between the catheter and the surrounding dilatation balloon material be consistent, fluid tight and of sufficient strength to withstand the fluid pressures involved in balloon dilatation. Typically the dilatation balloon is mounted along the distal end region of the catheter and surrounds the catheter. A main body portion or medial region of the balloon has a diameter substantially larger than that of the catheter, with proximal and distal shafts or neck regions of the balloon having inner diameters substantially equal to the outer diameter of the catheter. Proximal and distal tapered portions, or cones, join the medial region to the proximal and distal shafts, respectively, with each cone diverging in the direction toward the medial region. The bonds between the balloon and catheter are formed along the proximal and distal shafts.
One known bonding approach for heat fusible materials involves the resistance heating of copper jaws, while the jaws press the respective balloon shafts onto and against the catheter. One result of the deformation of the balloon and catheter material is the formation of small, random channels at the balloon/catheter interface, giving rise to variations in the strength of different bonds. To compensate for this variance, bonds are given a sufficient length to provide the requisite burst strength, typically axial dimensions in the range of about 0.070-0.150 inches. The copper jaws heat the balloon shafts and catheter primarily by conduction but also by radiation. The heat causes crystallization and stiffening of the balloon and catheter material, not only at the bond site, but also in both directions axially of the bond, due to heat conduction through the balloon and the catheter, and heat radiation from the jaws.
Several disadvantages arise from crystallization and stiffening at and around the bond. Stiffness along the catheter distal tip, distal balloon shaft and proximal bond area interferes with movement of the catheter along narrow and convoluted arteries, and increase the risk of trauma to the intima. To the extent that crystallization extends to the balloon tapered cones, catheter maneuverability is further reduced, and cone stiffness prevents a complete evacuation of radiopaque dye or other fluid from the balloon following dilatation.
Crystallization at the cones can be reduced or avoided by sufficient axial spacing between each of the balloon cones and its associated bond. However, this approach further increases the minimum required length of the distal balloon shaft. More particularly, it has been found that a gap of at least 0.030 inches between the bond and balloon cone is required, to satisfactorily reduce crystallization in the cone.
Other approaches to bonding avoid the use of copper jaws. For example, U.S. Pat. No. 4,251,305 (Becker et al) discloses a non-contact method for heat sealing a balloon onto a catheter. A length of thin tubing is slid over an elongated shaft of the catheter. Shrink tubing is installed over the thin walled tubing at its ends, and overlapping the shaft, and partially shrunk. Then, lamps provide further radiant energy to form gradually tapering thermoplastic joints that bond the tubing and shaft. The device employed for bonding utilizes three lamps that emit energy along the visible and infrared spectra. Each lamp is situated near an elliptical reflector, at one of the foci of the ellipse. The bond or treatment area is near the other focus. While this approach avoids the problems arising from mechanical squeezing from the copper jaws, the undesirable axial conductive heat transfer remains a problem.
Adhesives can be employed as an alternative to fusion bonding. However, the adhesive layers add to the thickness of the catheter and increase its rigidity at the region of the bonds. Moreover, adhesive bonds are known to be generally inferior to fusion bonds.
Therefore, it is an object of the present invention to provide a process for forming balloon catheters with fusion bonds, with minimal heat conduction away from the bond sites.
Another object of the invention is to bond dilatation balloons to catheters in a manner to reduce thermal shock to the balloon cones, resulting in softer, more flexible dilatation balloons.
A further object is to provide balloon catheters with proximal and distal fusion bonds that are narrow, yet able to withstand high burst pressures.
Yet another object is to provide a balloon catheter more maneuverable along arteries and at reduced risk of trauma to the arteries.